Fiber optic ferrule with smooth internal contours

ABSTRACT

A fiber optic ferrule includes a body extending from a first end to a second opposite end, with the body including an axial passage extending between the first and the second ends. The axial passage includes a first diameter portion having a diameter of at least 125 microns, a second diameter portion having a diameter of at least 250 microns and less than a diameter of a buffer, and a smooth and continuous transition between the first and the second diameter portions. The second diameter portion is positioned between the first diameter portion and the second end. The axial passage further defines a tapered shape at the second end extending inward from the second end toward the second diameter portion. In certain embodiments, another smooth and continuous transition can be provided between the taper shape and the second diameter portion. In certain embodiments, the axial passage is smooth and continuous between the first and the second ends of the body. A hub holds the ferrule. A method of assembling a terminated fiber optic cable is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/797,512,filed Oct. 30, 2017, now U.S. Pat. No. 10,295,757, which is acontinuation of Ser. No. 15/162,060, filed May 23, 2016, now U.S. Pat.No. 9,835,806, which is a continuation of Ser. No. 14/642,210, filedMar. 9, 2015, now U.S. Pat. No. 9,348,095, which is a continuation ofapplication Ser. No. 13/648,580, filed Oct. 10, 2012, now U.S. Pat. No.8,989,541, which application claims the benefit of U.S. ProvisionalPatent Application Ser. No. 61/545,444, filed Oct. 10, 2011, entitledDUAL INNER DIAMETER FERRULE DEVICE WITH SMOOTH INTERNAL CONTOURS ANDMETHOD, which applications are hereby incorporated by reference in theirentirety. This application is related to application Ser. No.15/332,854, filed Oct. 24, 2016, which is a continuation of applicationSer. No. 13/114,721, filed May 24, 2011, now U.S. Pat. No. 9,477,047,which is a continuation of application Ser. No. 12/271,335, filed Nov.14, 2008, now abandoned, which is a continuation of application Ser. No.11/972,373, filed Jan. 10, 2008, now U.S. Pat. No. 7,452,137, which is acontinuation of application Ser. No. 11/497,175, filed Aug. 1, 2006, nowU.S. Pat. No. 7,341,383, which applications are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present disclosure relates to terminating the ends of fiber opticcables with ferrules.

BACKGROUND OF THE INVENTION

Typically the end of a fiber optic cable is terminated by a fiber opticconnector by gluing the fiber within the cable to a ferrule of theconnector. A well known fiber optic cable size includes an inner glassfiber of 125 microns in diameter, with an outer coating of 250 micronsin diameter, covered by a polymeric buffer layer of 900 microns indiameter.

One problem with terminating fiber optic cables can include fiberbreakage at the rear interface area between the end of the glass fiberand the ferrule. In this interface area is the epoxy used to hold thefiber to the ferrule. Such breakage tends to increase in response togreater temperature fluctuations during use of the cables. Differencesin thermal expansion are believed to cause the breakage. There is a needto improve the interface between fiber optic cables and connectors toreduce fiber breakage, especially due to thermal stress.

SUMMARY OF THE INVENTION

A fiber optic ferrule includes a body extending from a first end to asecond opposite end, with the body including a smooth and continuousaxial passage extending between the first and second ends. The smoothand continuous axial passage includes a first diameter portion having adiameter of at least 125 microns and a second diameter portion having adiameter of at least 250 microns. The second diameter portion ispositioned between the first diameter and the second end. The smooth andcontinuous axial passage further defines a funnel shape at the secondend extending inward from the second end to the second diameter portion.The smooth and continuous axial passage further defines a firsttransition between the first and the second diameter portions and asecond transition between the second diameter portion and the funnelshape.

A method of assembling a terminated fiber optic cable includes providinga cable with an inner fiber at 125 microns, an outer coating at 250microns, and a buffer layer at 900 microns. The method includesstripping a portion of the coating from an end of the cable to expose aportion of the inner fiber, and stripping a portion of the buffer layerto expose a portion of the coating. The method further includesinserting the exposed fiber and the exposed coating into a smooth andcontinuous axial passage of a ferrule having first and second innerdiameters, wherein the first diameter is at least 125 microns, and thesecond diameter is at least 250 microns, and adhesively holding thefiber to the ferrule.

The present disclosure also relates to a device and method for mountinga fiber to a ferrule wherein the ferrule includes a first passagewayportion sized only to receive a bare fiber without a coating or a bufferlayer, a second passageway portion sized to receive the fiber includingthe coating, but no buffer layer, and a smooth and continuous transitionbetween the first and the second passageway portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of one embodiment of a ferrule anda hub in accordance with the principles of the present disclosure;

FIG. 2 is an end view of the ferrule and hub of FIG. 1;

FIG. 3 is a cross-sectional side view of the ferrule of FIG. 1;

FIG. 4 is a cross-sectional side view of the ferrule and hub of FIG. 1and includes a fiber optic cable inserted into the inner passage throughthe ferrule;

FIG. 5 is an enlarged cross-sectional view of a portion of the ferrule,hub, and cable of FIG. 4;

FIG. 6 is a cross-sectional side view of the ferrule and hub of FIG. 1and includes a fiber optic cable inserted into the inner passage throughthe ferrule with a fiber coating layer not as fully inserted into theferrule;

FIG. 7 is an enlarged cross-sectional view of a portion of the ferrule,hub, and cable of FIG. 6;

FIG. 8 is a cross-sectional side view of a prior art ferrule and hub;

FIG. 9 is a distal end view of an embodiment of a fiber optic connectorincluding another embodiment of a ferrule and a hub in accordance withthe principles of the present disclosure;

FIG. 10 is a cross-sectional side view of the fiber optic connector ofFIG. 9, as called out at FIG. 9;

FIG. 11 is an enlarged portion of FIG. 10;

FIG. 12 is an exploded perspective view of the fiber optic connector ofFIG. 9;

FIG. 13 is a distal end view of the ferrule of FIG. 9;

FIG. 14 is a distal end view of still another embodiment of a ferrule inaccordance with the principles of the present disclosure;

FIG. 15 is a partial side view of the ferrules of FIG. 9 and FIG. 14;

FIG. 16 is a cross-sectional side view of the ferrule of FIG. 9, ascalled out at FIG. 13;

FIG. 17 is a cross-sectional side view of the ferrule of FIG. 14, ascalled out at FIG. 14;

FIG. 18 is a partial cross-sectional side view of the ferrules of FIG. 9and FIG. 14, as called out at FIGS. 13 and 14, respectively;

FIG. 19 is the partial cross-sectional side view of FIG. 18, but withthe fiber optic cable of FIG. 4 overlaid and inserted into an innerpassage of the ferrule of FIG. 9 or 14;

FIG. 20 is the partial cross-sectional side view of FIG. 18, but withthe fiber optic cable of FIG. 4 overlaid and inserted into the innerpassage of FIG. 19 with the fiber coating layer of FIG. 6 not as fullyinserted into the ferrule of FIG. 9 or 14; and

FIG. 21 is a graph of a radius and a slope of the inner passage of FIG.19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1-7, a preferred embodiment of a fiber opticferrule 10 is shown mounted to a hub 12. Generally, ferrule 10 and hub12 are secured together by convenient methods including press fit oradhesive mounts. Ferrule 10 and hub 12 are mounted within a connectorhousing 13 shown in dashed lines in FIG. 1. Connector housing 13 can beone of a variety of well known connector types, including SC, FC, ST,LX.5, LC, and others. As will be described below, ferrule 10 and hub 12are connected to an end of a fiber optic cable for use in connectorizingthe end of the cable.

Ferrule 10 includes a body 16 with a first end 20 defining a ferruletip. Body 16 of ferrule 10 includes an opposite end 24 received in apocket 14 of hub 12. Ferrule 10 includes a central axis 28. First end 20of ferrule 10 is typically polished along with the fiber after the fiberis installed. Body 16 of ferrule 10 is typically ceramic inconstruction.

Ferrule 10 includes a central passage 30 concentric with axis 28.Central passage 30 extends from first end 20 to opposite end 24. Centralpassage 30 includes a first portion 34 having a first diameter, anintermediate or second portion 38 having a second diameter, and a rearor third portion 42. First portion 34 is sized to receive the innerfiber sized at 125 microns. Second portion 38 is sized to receive theportion of the cable including the outer coating at 250 microns. Thirdportion 42 is tapered inward from opposite end 24 so as to facilitateinsertion of the fiber during installation.

In prior art ferrules, such as ferrule 100 shown in FIG. 8, dualdiameters were not provided. In particular, the ferrule 100 of FIG. 8includes a central passage 130 having a uniform diameter sized forreceipt of the inner fiber at 125 microns. A tapered portion 132 extendsfrom end 134 to central passage 130.

In contrast, ferrule 10 includes dual diameter portions 34, 38, eachspecially sized to receive the inner fiber (125 microns) and a portionof the outer coating (250 microns), respectively.

Referring now to FIGS. 4 and 5, a fiber optic cable 50 is shown with aninner fiber 52, an outer coating 54, and a buffer layer 56. Fiber 52terminates at end 53. Typically, end 53 is removed and polished with end20 of ferrule 10. Coating 54 terminates at end 55. Buffer layer 56terminates at end 57. As shown, a portion of coating 54 extends beyondend 57 of buffer layer 56.

With special reference to FIG. 5, ferrule 10 closely surrounds fiber 52,and coating 54. Epoxy is used within central passage 30 to adhesivelyhold cable 50 to ferrule 10. However, very little epoxy is positionedaround end 55 of coating 54. By reducing the volume of epoxy positionedaround end 55 of coating 54, less thermally induced stresses are appliedto fiber 52. As shown, passage 30 defines a small conically shapedpocket 59 around end 55 of coating 54. Pocket 59 is the transition areabetween first and second portions 34, 38 of central passage 30. Byallowing coating 54 to extend past end 57 of buffer layer 56, and thenbe received in pocket 59, a smaller amount of epoxy is in contact withfiber 52 adjacent end 55 of coating 54. Less epoxy around the interfacebetween coating 54 and fiber 52 will reduce the thermal effects causedby any differences in thermal expansion between fiber 52 and the epoxy.

Coating 54 does not need to be fully inserted into ferrule 10, as shownin FIGS. 4 and 5. As shown in FIGS. 6 and 7, pocket 59 is larger aroundthe end 55 of coating 54. Such an arrangement still provides less epoxyaround fiber 52, than in the arrangement of FIG. 8. One example epoxy isF123 from Tra-con, Inc. of Bedford, Mass.

In ferrule 10, first portion 34 has a first dimension sized large enoughto receive the uncoated fiber, but not so large as to receive the coatedfiber. Second portion 38 has a second dimension large enough to receivethe coated fiber, but not so large as to receive the buffer.

In the illustrated embodiment, first portion 34 is cylindrically shapedand sized at 0.1255 mm+/−0.0015/0.0000 mm to receive the inner fibersized at 125 microns. Second portion 38 is cylindrically shaped andsized at 0.260 mm+/−0.010 mm to receive the portion of the cableincluding the outer coating at 250 microns. A preferred range for secondportion 38 is greater than 250 microns, and less than or equal to 500microns. A more preferred range for second portion 38 is greater than250 microns, and less than or equal to 300 microns. In the illustratedembodiment, ferrule 10 is 10.5 mm long, with second portion 38 extendinginto ferrule 10 about 3 mm from end 24.

Referring now to FIGS. 9-13, 15, 16, and 18-21, a preferred embodimentof a fiber optic connector 200, including a fiber optic ferrule 210, isshown. The fiber optic ferrule 210 is mounted to a hub 212 of the fiberoptic connector 200 (see FIGS. 10-12). In other preferred embodiments, afiber optic ferrule 210′, illustrated at FIGS. 14, 15, and 17-21, can bemounted to the hub 212 of the fiber optic connector 200. Hereinafter,unless noted otherwise, the fiber optic ferrule 210 and the fiber opticferrule 210′ will be collectively referred to as the fiber optic ferrule210.

Generally, the fiber optic ferrule 210 and the hub 212 are securedtogether by convenient methods including press fit or adhesive mounts.In certain preferred embodiments, the hub 212 is a plastic material thatis overmolded onto the ferrule 210. The fiber optic ferrule 210 and thehub 212 are mounted within a connector housing 213, shown at FIGS. 9-12.In the depicted embodiment, the connector housing 213 is an SC typeconnector housing, and the fiber optic connector 200 is an SC type fiberoptic connector. In other embodiments, the fiber optic connector 200 canbe one of a variety of well-known connector types, including FC, ST,LX.5, LC, and others. As described above, with respect to the ferrule 10and the hub 12, the ferrule 210 and the hub 212 are connected to the endof the fiber optic cable 50 for use in connectorizing the end of thefiber optic cable 50.

As illustrated at FIGS. 10-12, the fiber optic connector 200 may furtherinclude a release sleeve 202, a spring 204, a proximal member 206,and/or a cable strain relief member 208. As illustrated at FIGS. 16 and17, the ferrule 210 includes a body 216 with a first end 220 defining aferrule tip. The body 216 of the ferrule 210 includes an opposite end224 received in a pocket 214 of the hub 212 (see FIG. 11). The ferrule210 includes a central axis 228. The first end 220 of the ferrule 210 istypically polished along with the fiber 52 after the fiber 52 isinstalled. The body 216 of the ferrule 210 is typically ceramic inconstruction.

In certain preferred embodiments, the body 216 of the ferrule 210 ismade of yttria-stabilized zirconium-oxide, yttria-stabilized zirconia,YSZ, Y₂O₃ stabilized ZrO₂, etc. In certain preferred embodiments, thebody 216 of the ferrule 210 is molded. By molding the ferrule 210,internal features can be included within the ferrule 210. The internalfeatures can be smooth and continuous and include curvature. The smoothand continuous internal features can be produced at a lower cost than byalternative methods, such as machining. In certain preferredembodiments, the body 216 of the ferrule 210 has a crystal structurethat is 100% tetragonal. In certain preferred embodiments, the body 216of the ferrule 210 has a maximum average grain size of about 0.5microns. In certain preferred embodiments, the body 216 of the ferrule210 has a hardness (HV10) of about 1100-1600. In certain preferredembodiments, the body 216 of the ferrule 210 has a Young's modulus ofabout 30,000,000 pounds per square inch. In certain preferredembodiments, the body 216 of the ferrule 210 has a flexural strength ofabout 1,000,000,000 Pascals. In certain preferred embodiments, the body216 of the ferrule 210 has a density of about 6 grams per cubiccentimeter. In certain preferred embodiments, the body 216 of theferrule 210 has a coefficient of linear thermal expansion of about10.6×10⁻⁶/degrees Celsius between 40 degrees Celsius and 40 degreesCelsius and a coefficient of linear thermal expansion of about11.0×10⁻⁶/degrees Celsius between 400 degrees Celsius and 800 degreesCelsius.

The ferrule 210 includes a central passage 230 concentric with the axis228. The central passage 230 extends from the first end 220 to theopposite end 224. The central passage 230 includes a first portion 234having a first diameter D₁ (see FIGS. 16 and 17), an intermediate orsecond portion 238 having a second diameter D₂ (see FIG. 18), and a rearor third portion 242. In certain preferred embodiments, the centralpassage 230 is molded into the body 216 of the ferrule 210. In otherembodiments, the central passage 230 is machined into the body 216 ofthe ferrule 210.

As with the first portion 34 mentioned above, the first portion 234 issized to receive the inner fiber 52, sized at 125 microns, (see FIGS. 19and 20). As with the second portion 38 mentioned above, the secondportion 238 is sized to receive the portion of the fiber optic cable 50including the outer coating 54 at 250 microns. As with the third portion42 mentioned above, the third portion 242 is tapered inwardly from theopposite end 224 so as to facilitate insertion of the fiber 52 duringinstallation. By having the smooth and continuous central passage 230,scratching and scoring of the inner fiber 52 and the outer coating 54can be eliminated or substantially reduced. The scratching and scoringof the inner fiber 52 and/or the outer coating 54 can produce defectsthat can grow into fatigue cracks and lead to failure of the fiber 52.In a preferred embodiment, the third portion 242 is sized at a thirddiameter D₃ (see FIG. 18) of about 1.2 millimeters+/−0.1 millimeter andforms an angle α of about 60 degrees+/−3 degrees centered about thecentral axis 228. In other embodiments, the third diameter D₃ may rangefrom about 0.5 millimeter to about 1.5 millimeters. In otherembodiments, the angle α may range from about 60 degrees+/−30 degrees.In other embodiments, the angle α may range from about 60 degrees+/−15degrees.

In contrast with certain prior art ferrules 100 (see FIG. 8), theferrule 210 includes dual diameter portions 234, 238, each speciallysized to receive the inner fiber 52 (125 microns) and a portion of theouter coating 54 (250 microns), respectively.

As illustrated at FIGS. 4, 5, 19, and 20, the fiber optic cable 50includes the inner fiber 52, the outer coating 54, and the buffer layer56. The inner fiber 52 terminates at the end 53. Typically, the end 53is removed and polished with the end 220 of the ferrule 210. The coating54 terminates at the end 55. The buffer layer 56 terminates at the end57. As shown, a portion of the coating 54 extends beyond the end 57 ofthe buffer layer 56. In certain preferred embodiments, the inner fiber52 is made of silica and has a Young's modulus of about 70.3 GPa(10,000,000 pounds per square inch 10⁶). In certain preferredembodiments, the inner fiber 52 has a coefficient of thermal expansionof about 5×10⁻⁷/degrees Celsius. In certain preferred embodiments, thecoating 54 includes an inner coating that has a Young's modulus of about1-5 MPa and an outer coating that has a Young's modulus of about 800MPa.

With special reference to FIG. 19, ferrule 210 closely surrounds thefiber 52, and the coating 54. Epoxy is used within the central passage230 to adhesively hold the cable 50 to the ferrule 210. However, alimited amount of the epoxy is positioned around the end 55 of thecoating 54, and is shaped by the central passage 230 of the ferrule 210.As will be described in detail below, by prescribing a shape of theepoxy and/or by reducing the volume of the epoxy positioned around theend 55 of the coating 54, less thermally induced stresses, includingfatiguing cyclical stresses, are applied to the fiber 52. As shown, thepassage 230 defines a small pocket 259 around the end 55 of the coating54. The pocket 259 is a transition area between the first and the secondportions 234, 238 of the central passage 230 and is smoothly shaped bythe central passage 230. By allowing the coating 54 to extend past theend 57 of the buffer layer 56, and then be received in the pocket 59, alimited amount of the epoxy is in contact with the fiber 52 adjacent theend 55 of the coating 54. Limited epoxy around the interface between thecoating 54 and the fiber 52 will reduce the thermal effects caused byany differences in thermal expansion between the fiber 52, the ferrule210, and the epoxy.

The coating 54 does not need to be fully inserted into the ferrule 210,as shown at FIG. 19. As shown at FIG. 20, a pocket 259′ further includesa portion of the second portion 238 and therefore is larger around theend 55 of the coating 54. Such an arrangement still provides less of theepoxy around the fiber 52, than in the arrangement of FIG. 8.

One example epoxy is F123 from Henkel of Dusseldorf, Germany. Anotherexample epoxy is EPO-TEK® 383ND from Epoxy Technology, Inc. ofBillerica, Mass. 01821. The epoxy, when cured, has a coefficient ofthermal expansion of about 34×10⁻⁶/degrees Celsius below a glasstransition temperature of about 100 degrees Celsius and a coefficient ofthermal expansion of about 129×10⁻⁶/degrees Celsius above the glasstransition temperature. The epoxy has a storage modulus of about 369,039pounds per square inch.

In the ferrule 210, the first portion 234 has a first dimension sizedlarge enough to receive the uncoated fiber 52, but not so large as toreceive the coated fiber. The second portion 38 has a second dimensionlarge enough to receive the coated fiber, but not so large as to receivethe buffer layer 56.

In the illustrated embodiment, the first portion 234 is cylindricallyshaped, and the first diameter D₁ is sized at 0.1255millimeter+/−0.0010/0.0000 millimeter to receive the inner fiber 52,sized at about 125 microns. The second portion 238 is cylindricallyshaped, and the second diameter D₂ is sized at 0.27 millimeter+/−0.02millimeter/0.00 millimeter to receive the portion of the cable 50including the outer coating 54 at about 250 microns. A preferred rangefor the second diameter D₂ of the second portion 238 is greater than 245microns and less than or equal to 500 microns. A more preferred rangefor the second diameter D₂ of the second portion 238 is greater than 260microns and less than or equal to 400 microns. An even more preferredrange for the second diameter D₂ of the second portion 238 is greaterthan 260 microns and less than or equal to 300 microns.

In the illustrated embodiment, a length L₁ (see FIGS. 16 and 17) of theferrule 210 is about 10.5 millimeters+/−0.05 millimeters long, with thesecond portion 238 extending into the ferrule 210 by a length L₂ (seeFIG. 18) of about 2.21 millimeters+/−0.1 millimeters from the end 224.In other embodiments, the length L₂ may range from about 5 millimetersto about 1 millimeter. In the illustrated embodiment, the second portion238 starts at a length L₃ (see FIG. 18) of about 1.21 millimeters+/−0.1millimeters from the end 224. In other embodiments, the length L₃ mayrange from about 4 millimeters to about 0.5 millimeter. In theillustrated embodiment, the third portion 242 extends between the end224 and a length L₄ (see FIG. 18) of about 0.4573 millimeters+/−0.1millimeters from the end 224. In other embodiments, the length L₄ mayrange from about 2 millimeters to about 0.2 millimeter. In theillustrated embodiment, the first portion 234 extends between the end220 and a length L₅ (see FIG. 18) of about 2.6771 millimeters+/−0.1millimeters from the end 224. In other embodiments, the length L₅ mayrange from about 5.5 millimeters to about 0.7 millimeter.

According to the principles of the present disclosure, the centralpassage 230 of the fiber optic ferrule 210 is smooth and continuous.FIG. 21 includes a graph of a radius R from the central axis 228 to aninterior surface S (see FIG. 18) of the central passage 230 as thecentral passage 230 extends along the length L₁ from the end 224 to theend 220. The radius R is smooth and continuous along the length L₁ fromthe end 224 to the end 220. FIG. 21 also includes a graph of a slope γfrom the central axis 228 to the interior surface S (see FIG. 18) of thecentral passage 230 as the central passage 230 extends along the lengthL₁ from the end 224 to the end 220. The slope γ is continuous along thelength L₁ from the end 224 to the end 220. By having the smooth andcontinuous radius R and the continuous slope γ, stress concentrationsimposed on the fiber 52 can be substantially reduced. In particular, theepoxy bonds the fiber 52 to the central passage 230 of the fiber opticferrule 210 and may impose the stress concentrations on the fiber 52. Byhaving the smooth and continuous radius R and the continuous slope γ,stress concentrations imposed on the outer coating 54 can besubstantially reduced. In particular, the epoxy bonds the outer coating54 to the central passage 230 of the fiber optic ferrule 210 and mayimpose the stress concentrations on the outer coating 54 and thereby tothe fiber 52 which is mechanically joined to the outer coating 54. Thestress concentrations can be generated by thermal stress fromdifferential thermal expansion between the fiber 52, the epoxy, and/orthe fiber optic ferrule 210. The stress concentrations can also begenerated by mechanical loads including shock and vibration. The stressconcentrations can also be generated by shrinkage or expansion of theepoxy as it cures. The stress concentrations can also be generated bychanges in a radial thickness t of the epoxy (see FIG. 19). Inparticular, the radial thickness t of the epoxy is very small in thefirst portion 234 of the central passage 230. The small radial thicknesst of the epoxy may result in a relatively high radial stiffness of theepoxy in the first portion 234 of the central passage 230 compared witha lower radial stiffness of the epoxy in the pocket 259. By having thesmooth and continuous radius R and the continuous slope γ, thicknesschange of the radial thickness t of the epoxy also changes smoothly fromthe first portion 234 of the central passage 230 and into the pocket259. By having the smooth and continuous radius R and the continuousslope γ, stiffness change of the radial stiffness of the epoxy alsochanges smoothly from the first portion 234 of the central passage 230into the pocket 259. The smooth stiffness change of the radial stiffnessof the epoxy may also substantially reduce the stress concentration.

To provide the smooth and continuous central passage 230 of the fiberoptic ferrule 210, a first transition 300 is included between the firstportion 234 and the second portion 238, and a second transition 310 isincluded between the second portion 238 and the third portion 242 (seeFIGS. 18 and 21). The first transition 300 includes a first segment 302that includes a first radius R₁ depicted at about 1 millimeter. In otherembodiments, the first radius R₁ can range from about 0.2 millimeter toabout 1.5 millimeters. The first transition 300 includes a secondsegment 304 that is linear and is sloped relative to the central axis228 by an angle β. As depicted, the angle β is 15 degrees. In otherembodiments, the angle β can range from about 5 degrees to about 20degrees or from about 5 degrees to about 45 degrees. The firsttransition 300 includes a third segment 306 that includes a secondradius R₂ depicted at about 0.5 millimeter. In other embodiments, thesecond radius R₂ can range from about 0.2 millimeter to about 1.5millimeters. The second transition 310 includes a third radius R₃depicted at about 1.5 millimeters. In other embodiments, the thirdradius R₃ can range from about 0.2 millimeter to about 4.5 millimeters.

In certain embodiments, the transition 300 is provided, and the secondtransition 310 may be deleted. In these embodiments, the central passage230 may not be completely smooth and continuous along the length L₁. Thetransition 300 facilitates smoothing out differences in thermalexpansion and stiffness between the fiber optic ferrule 210, the innerfiber 52, and the epoxy. The transition 300 thereby protects the innerfiber 52 by reducing stress concentrations. In certain embodiments, theouter coating 54, where present, may accommodate differences in thermalexpansion and stiffness between the fiber optic ferrule 210, the innerfiber 52, and the epoxy and may thereby offer some protection fromstress concentrations.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

What is claimed is:
 1. A fiber optic ferrule and cable comprising: aferrule body extending from a first end to an opposite second end, theferrule body having an outer cylindrical shape, the ferrule bodyincluding a smooth and continuous axial passage extending between thefirst and the second ends of the ferrule body, the smooth and continuousaxial passage of the ferrule body including: a first diameter portiongenerally cylindrical in shape adjacent the first end of the ferrulebody; a second diameter portion generally cylindrical in shapepositioned between the first diameter portion and the second end of theferrule body; and a smooth and continuous transition area extendingbetween and adjoining the first and the second diameter portions; anoptical fiber cable including an inner fiber, an outer coating, and abuffer layer, the outer coating positioned around the inner fiber andthe buffer layer positioned around the outer coating, a portion of theouter coating and inner fiber extending beyond an end of the bufferlayer and a portion of the inner fiber extending beyond an end of theouter coating; and a hub mounted around the second end of the ferrulebody, the hub including an axial passage; wherein the first diameterportion of the smooth and continuous axial passage of the ferrule bodyreceives the inner fiber of the optical fiber cable; wherein the seconddiameter portion of the smooth and continuous axial passage of theferrule body receives the outer coating of the optical fiber cable;wherein the end of the buffer layer of the optical fiber cable ispositioned in the axial passage of the hub; wherein the smooth andcontinuous axial passage of the ferrule body includes an interiorsurface; and wherein a slope of the interior surface is continuous alongthe length of the ferrule body from the first end of the ferrule body tothe opposite second end of the ferrule body.
 2. The fiber optic ferruleand cable of claim 1, wherein the ferrule body is molded of a ceramicmaterial.
 3. The fiber optic ferrule and cable of claim 2, wherein theceramic material has a maximum average grain size of 0.5 microns and acoefficient of linear thermal expansion of about 10.6×10⁻⁶/degreesCelsius.
 4. The fiber optic ferrule and cable of claim 1, wherein thefirst diameter portion of the smooth and continuous axial passage of theferrule body has a diameter of about 125 microns.
 5. The fiber opticferrule and cable of claim 1, wherein the end of the buffer layer of theoptical fiber cable is positioned in the smooth and continuoustransition area.
 6. The fiber optic ferrule and cable of claim 1,wherein the end of the buffer layer of the optical fiber cable ispositioned adjacent the smooth and continuous transition area.
 7. Thefiber optic ferrule and cable of claim 1, wherein the end of the bufferlayer of the optical fiber cable is spaced from the smooth andcontinuous transition area.
 8. The fiber optic ferrule and cable ofclaim 1, further comprising an adhesive material within the smooth andcontinuous axial passage of the ferrule body holding the optical fibercable to the ferrule body.
 9. The fiber optic ferrule and cable of claim8, wherein the smooth and continuous transition area defines a pocketthat limits an amount of the adhesive material in contact with theoptical fiber adjacent the end of the coating and thereby reduces stressconcentration imposed on the optical fiber.
 10. The fiber optic ferruleand cable of claim 1, wherein an angle of the interior surface of thesmooth and continuous axial passage relative to a central axis of theferrule body varies along the length of the ferrule body between aminimum of about 0 degrees and a maximum of about 30 degrees.
 11. Thefiber optic ferrule and cable of claim 10, wherein a radial distance ofthe interior surface of the smooth and continuous axial passage from thecentral axis of the ferrule body varies along the length of the ferrulebody between a minimum of about 62.5 microns and a maximum of about 600microns.
 12. The fiber optic ferrule and cable of claim 1, wherein aradial distance of the interior surface of the smooth and continuousaxial passage from a central axis of the ferrule body varies along thelength of the ferrule body between a minimum of about 62.5 microns and amaximum of about 600 microns.
 13. A fiber optic ferrule comprising: aferrule body extending from a first end to an opposite second end, theferrule body having an outer cylindrical shape, the ferrule bodyincluding a smooth and continuous axial passage extending between thefirst and the second ends of the ferrule body, the smooth and continuousaxial passage of the ferrule body including: an interior surface; afirst diameter portion generally cylindrical in shape adjacent the firstend of the ferrule body; a second diameter portion generally cylindricalin shape positioned between the first diameter portion and the secondend of the ferrule body; and a smooth and continuous transition areaextending between and adjoining the first and the second diameterportions; and wherein a slope of the interior surface is continuousalong the length of the ferrule body from the first end of the ferrulebody to the second end of the ferrule body.
 14. The fiber optic ferruleof claim 13, wherein the ferrule body is molded of a ceramic material.15. The fiber optic ferrule of claim 14, wherein the ceramic materialhas a maximum average grain size of 0.5 microns and a coefficient oflinear thermal expansion of about 10.6×10⁻⁶/degrees Celsius.
 16. Thefiber optic ferrule of claim 13, wherein the first diameter portion ofthe smooth and continuous axial passage of the ferrule body has adiameter of about 125 microns.
 17. The fiber optic ferrule of claim 13,wherein an angle of the interior surface of the smooth and continuousaxial passage relative to a central axis of the ferrule body variesalong the length of the ferrule body between a minimum of about 0degrees and a maximum of about 30 degrees.
 18. The fiber optic ferruleof claim 17, wherein a radial distance of the interior surface of thesmooth and continuous axial passage from the central axis of the ferrulebody varies along the length of the ferrule body between a minimum ofabout 62.5 microns and a maximum of about 600 microns.
 19. The fiberoptic ferrule of claim 13, wherein a radial distance of the interiorsurface of the smooth and continuous axial passage from a central axisof the ferrule body varies along the length of the ferrule body betweena minimum of about 62.5 microns and a maximum of about 600 microns.